1. Field of the Invention
The present invention relates to an automatic bending apparatus and more particularly, to an automatic bending apparatus having a wide universality in which a plate such as an iron plate is supplied to a press brake type bending machine whereby the plate is bent and then taken out.
2. Description of the Prior Art
Conventionally, bending of plates such as iron plates etc. was performed using a press brake type bending machine or the like controlled by operators. Accordingly, such a bending operation was made extremely inefficiently and needed many operators.
Therefore, the applicant of the present invention proposed previously automatic bending apparatus comprising a robot working in association with a press brake type bending machine so that bending of a plate can be automatically performed. Such proposed automatic bending apparatus are disclosed, for example, in Japanese Patent Laying-Open Gazette No. 130463/1979 laid open on Oct. 9, 1979, Japanese Patent Laying-Open Gazette No. 48425/1980 laid open on Apr. 7, 1980, Japanese Patent Laying-Open Gazette No. 54215/1980 laid open on Apr. 21, 1980 and Japanese Patent Laying-Open Gazette No. 39121/1980 laid open on Oct. 30, 1980, etc. Particularly in Japanese Laying-Open Gazette No. 39121/1980, control of a robot is disclosed in a concrete manner.
In any of the above mentioned conventional automatic bending apparatus, a work piece or a plate is positioned with respect to a bending machine by holding the plate by means of a gripper. However, an end portion of a plate in the horizontal state often rises as a top die is lowered and accordingly, bending operation cannot be made in the state in which the plate is held by the gripper. Although for such automatic bending apparatus, there is also a type in which a bottom die is lifted, the same problem as described above is also involved in this type.
In order to dissolve the above described problem, conventionally a method is adopted in which a plate is first positioned and is held by a gripper until a top die comes in contact with the plate and then the gripper is detached and the top die is further lowered to bend the plate. Then, according to this method, the bent plate is appropriately held again by the gripper and the top die is lifted and subsequently, the plate is further positioned by the gripper for another bending process or released when the bending process is completed. In such a conventional method, it becomes necessary to set free the plate from the state held by the gripper or to shift the grasp by the gripper from one position to another on the plate. However, in certain kinds of plates, plastic deformation or deflection would be caused during bending operation and accordingly, the position to be newly grasped by the gripper would become unclear and deviate from the initially grasped position. It follows that a product in a shape erroneously bent is obtained. Therefore, it is preferable not to remove the gripper from the work piece or not to shift the hold by the gripper from one position to another during the bending process as far as possible.